On a portion where an injector is mounted to a cylinder head for an engine, a sealing device is provided in order to prevent leakage of high-pressure combustion gas from an annular gap between a mounting hole formed in the cylinder head and the injector. In addition, on a portion where mounted components such as various sensors are mounted to the cylinder head, the sealing device is provided similarly, as well. In such a sealing device, there is known a technique which employs a seal ring made of resin which has a small number of components and is capable of suppressing noises caused by vibrations as compared with the case where a metal washer-like seal is used (see Patent Literature 1).
However, the seal ring made of resin has a problem that a squeeze on an outer peripheral surface side is reduced over time due to creep deformation, thereby deteriorating its sealing function.